Valve lifters are commonly used in internal combustion engines to convert rotational motion of an engine cam into linear motion, for controlling the position of gas exchange valves. A typical design includes a lifter body coupled with a pushrod configured to actuate a rocker arm of one or more gas exchange valves. The lifter body includes a roller positioned in contact with the engine cam, such that rotation of the engine cam causes the valve lifter to slide within a lifter bore formed in the engine housing. Sliding of the valve lifter adjusts the pushrod, which in turn moves the rocker arm in a well-known manner.
In certain designs, valve lifters may become misaligned with the cam via rotation of the valve lifter within the lifter bore. The causes of such misalignment appear to vary from engine to engine. Even seemingly identical engine designs can exhibit different misalignment issues of their valve lifters over the course of the engine's service life. Adding to the complexity, some valve lifters tend to rotate more, or differently than other valve lifters even within the same engine.
Various strategies have been proposed over the years to limit rotation of valve train components. One technique employs an insert received in a space between adjacent valve train tappets. Great Britain Patent No. 999,507 to Price discloses such a design, where guiding faces on the insert cooperate with the tappets to restrain them against rotation in their bores. The design purportedly enables fuel-injection pumps to be constructed so that the distance between tappet bores is reduced. While Price may achieve its stated purposes, it is not without drawbacks, and appears purpose-built to solve problems which may be specific to certain reciprocating tappet systems.